1. Field of the Invention
The invention relates to an electronic welding current generator.
2. Description of the Related Art
The real arc voltage cannot be directly measured as an actual value for the purpose of regulating the pulse voltage, since an electric contact on the arc is not possible. Therefore, in most cases, the actual voltage value is measured at the output clamps of the welding current source.
The nominal value U.sub.p of the pulse voltage is adjusted also under consideration of the other relevant parameters until the welding process runs optimally. The active arc voltage is thereby smaller than the controlled generator output voltage. The difference results from the voltage drop along the welding cables and the voltage drop at the contact nozzle.
These voltage drops increase with time due to an increase in resistance of the warming welding cables and the wear of the contact nozzle. The voltage available at the arc decreases accordingly, the arc shortens and the splatter frequency increases until complete derailment of the process.
The arc length, which has the tendency to decrease, can be manually corrected and, thus, maintained constant in the desired manner, by observing the arc length and correspondingly increasing the nominal value of the pulse voltage U.sub.p. However, this method is too demanding on the operating personnel and rules itself out for reasons of cost and missing quality control.
Consequently, in practical operation, one acts according to experience. On principle, after a set number of welding cycles, the contact nozzle is replaced, just in case. Although this method is practically workable, it leads to a high nozzle consumption and to relatively long down times and, thus, to preventable, high cost.
Since with time, this, i.e., increasing detrimental voltage drop at the contact nozzle and warming of the welding cables, is only significant in the pulse voltage phase, i.e., is generated during the pulse voltage phase t.sub.p, it would be appropriate to use the principle of I.sub.P -I.sub.G modulation instead of the U.sub.P -I.sub.G modulation, since constant currents generate constant voltage drops at the process resistor. However, since the so-called "inner control" of the U.sub.P -I.sub.G modulation is not present, the process stability must be forced by way of pulse time control (t.sub.p control). This method without doubt prolongs nozzle life, but, as can be shown, leads to lower welding quality.